Silent Commander Tann?

[Fomalhaut]

Not the same problem others have encountered.

Since, at the Graveyard, Tann kept on ranting about being weak, I took him back to the Fort. We faced Vallis, he got hanged, Tann is now standing where Vallis used to, okay. And since then... when I try to talk to Tann, he just stands there, utterly silent, turns to me, that's all. I dealt with the bandits - he stays silent. Have yet to finish the Graveyard, though, but him and the other soldiers just won't talk to me now.

[Loki[D.d.G]]

First, the obligatory; Are you fully patched?

If so, have you tried right-clicking on Tann to access the NPC menu where you can pickpocket/examine and select the "Talk To" option from there?